/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.io.hdfs;



import com.fasterxml.jackson.core.JsonGenerator;

import com.fasterxml.jackson.core.JsonParser;

import com.fasterxml.jackson.core.type.TypeReference;

import com.fasterxml.jackson.databind.*;

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;

import com.fasterxml.jackson.databind.annotation.JsonSerialize;

import com.fasterxml.jackson.databind.module.SimpleModule;

import com.google.auto.service.AutoService;

import org.apache.hadoop.conf.Configuration;



import java.io.IOException;

import java.util.Map;

import java.util.TreeMap;



/**

 * A Jackson {@link Module} that registers a {@link JsonSerializer} and {@link JsonDeserializer} for

 * a Hadoop {@link Configuration}. The serialized representation is that of a JSON map.

 *

 * <p>Note that the serialization of the Hadoop {@link Configuration} only keeps the keys and their

 * values dropping any configuration hierarchy and source information.

 */

@AutoService(Module.class)

public class HadoopFileSystemModule extends SimpleModule {

  public HadoopFileSystemModule() {

    super("HadoopFileSystemModule");

    setMixInAnnotation(Configuration.class, ConfigurationMixin.class);

  }



  /** A mixin class to add Jackson annotations to the Hadoop {@link Configuration} class. */

  @JsonDeserialize(using = ConfigurationDeserializer.class)

  @JsonSerialize(using = ConfigurationSerializer.class)

  private static class ConfigurationMixin {}



  /** A Jackson {@link JsonDeserializer} for Hadoop {@link Configuration} objects. */

  private static class ConfigurationDeserializer extends JsonDeserializer<Configuration> {

    @Override

    public Configuration deserialize(

        JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {

      Map<String, String> rawConfiguration =

          jsonParser.readValueAs(new TypeReference<Map<String, String>>() {});

      Configuration configuration = new Configuration(false);

      for (Map.Entry<String, String> entry : rawConfiguration.entrySet()) {

        configuration.set(entry.getKey(), entry.getValue());

      }

      return configuration;

    }

  }



  /** A Jackson {@link JsonSerializer} for Hadoop {@link Configuration} objects. */

  private static class ConfigurationSerializer extends JsonSerializer<Configuration> {

    @Override

    public void serialize(

        Configuration configuration,

        JsonGenerator jsonGenerator,

        SerializerProvider serializerProvider)

        throws IOException {

      Map<String, String> map = new TreeMap<>();

      for (Map.Entry<String, String> entry : configuration) {

        map.put(entry.getKey(), entry.getValue());

      }

      jsonGenerator.writeObject(map);

    }

  }

}